This invention relates to a method and apparatus for recovering heat and solvent from the hot solvent saturated air in drying ovens of the type utilized to dry solvent base and paint coatings on various articles by applying hot dry air to the articles.
Solvent base paints and coatings usually contain about 50% organic solvents which evaporate from the paint or coating during the drying process after the paint or coating has been applied to an article. In many industrial painting and coating processes the articles are painted or coated and then placed in a drying oven where hot dry air is applied to the article to accelerate the drying procedure. When the air in the oven becomes saturated with solvent, the air must be exhausted and a new supply of hot dry air supplied to the oven to continue the drying process.
When the saturated air is exhausted from the oven to the atmosphere, a substantial amount of solvent and heat is wasted, and the solvent is usually considered to be an atmospheric pollutant. Additionally, the flammability of the solvent tends to create a fire hazard in and about the manufacturing plant.
In order to comply with government pollution control regulations which recently have been established, some industrial painting and coating plants have been equipped with thermal fume incinerators for burning the exhaust gases from paint and coating drying ovens. The thermal incinerators usually require temperatures in excess of 1200.degree. F. in order to ignite the solvent vapor, and usually include a structure that supplies an auxiliary fuel to the oven exhaust gases, such as natural gas, to cause incineration of the solvent fumes. Of course, this requires even additional energy.
In order to avoid the waste of heat energy and in order to avoid expelling solvent vapor to the atmosphere as a pollutant, it is desirable to extract both the heat and solvent vapor from the air exhausted from a drying oven.